Video camera with a function to correct defective pixels of solid state image pickup device and method of correcting defective pixels of solid state image

ABSTRACT

When defective pixels of a solid state image pickup device of a video camera are corrected by signal processes, a white spot noise is detected by closing an iris and by comparing the signal level and a level of only a dark current. Further, in this case, a gain of an AGC circuit for controlling a gain of a video signal is raised and a precise detection is executed. By executing such a detecting operation at the time of turn-on or turn-off of a power source, the user is not annoying. In the ordinary photographing, a reference level in detection of a white spot noise is set to an optimum value in accordance with a temperature of the solid state image pickup device or its peripheral temperature or the gain of the AGC circuit so that the white spot noise detection is not influenced by the temperature of the solid state image pickup device or the operating state of the AGC circuit.

This application is a continuation application of Ser. No. 08/249,286,filed May 25, 1994, now abandoned.

BACKGROUND OF THE INVENTION

The invention relates to a video camera using a solid state image pickupdevice and, more particularly, to a function to correct defective pixelsof a solid state image pickup device by signal processes.

As a conventional video camera having a function to correct defectivepixels of a solid state image pickup device, for example, a video cameradisclosed in JP-A-3-236689 can be mentioned. According to such a videocamera, after an image signal obtained by the solid state image pickupdevice was converted into a digital signal, in order to correct anabnormal signal of an image, what is called a white spot noise, due todefective pixels, whether the level of the absolute value of an outlinecorrection signal is equal to or larger than a predetermined value ornot is discriminated by using an outline correction circuit, therebyautomatically judging whether the pixels are defective pixels or not.

Although the solid state image pickup device converts an energy of lightinto an electric signal, it has a nature to also convert a thermalenergy into an electric signal. The signal component which was convertedinto the electric signal by such a thermal energy is caused by a darkcurrent. Since the dark current occurs by the thermal energy, atemperature dependency is strong and its value is almost doubled whenthe temperature rises by 10° C.

A white spot noise occurs when the dark current is abnormally increasedas compared with the other pixels due to defective pixels. Therefore,the signal level of the white spot noise has a temperature dependency.Since the video camera executes an automatic gain control (AGC), when anobject is dark, a gain of circuit system is raised, thereby keeping abrightness of a video image constant. Thus, the level of white spotnoise is also changed by the gain of the AGC. Further, since a changesimilarly occurs with regard to the normal signal component, it is verydifficult to detect the white spot noise in the ordinary photographingstate. In the above literature, however, a judgment reference of thewhite spot noise is merely set to a predetermined value, so that noconsideration is made in the conventional video camera with respect to apoint that the white spot noise due to defective pixels is detected at ahigh precision.

Reference may further be made to U.S. Pat. No. 4,654,714 which relatesto correction of white spot noise.

SUMMARY OF THE INVENTION

It is the first object of the present invention that a white spot noisedue to defective pixels of a solid state image pickup device is detectedat a high precision by a video camera iself and the correction of thewhite spot noise based on it is satisfactorily executed.

To accomplish the above object, according to a video camera of theinvention, when the defective pixels of the solid state image pickupdevice is corrected by a signal process, the white spot noise isdetected in a closed state of an iris. Therefore, the level comparisoncan be performed by only the signal due to the dark current and aninfluence by the object is eliminated. In the above detection, when again of an AGC circuit to perform a gain control of a video signal israised, the white spot noise can be more precisely detected. Byexecuting such a detecting operation at the time of power-on orpower-off, the user is not inconvenienced or annoyed.

The second object of the invention is to accurately detect a white spotnoise due to defective pixels of a solid state image pickup deviceduring the photographing operation and to preferably correct the whitespot noise based on it.

To accomplish the above object, according to a video camera of thepresent invention, when the defective pixels of the solid state imagepickup device are corrected by signal processes, a threshold level forjudgment of the white spot noise is set to an optimum value inaccordance with a temperature of the solid state image pickup device orits peripheral portion or with the gain of the AGC circuit and the whitespot noise is detected by using such a level. For example, when thetemperature rises by 10° C., the threshold level for judgment of thewhite spot noise is doubled. When the temperature drops by 10° C., thethreshold level is reduced into 1/2. When the gain of the AGC circuit isdoubled, the threshold level for judgment of the white spot noise isdoubled. When the gain of the AGC circuit is reduced into 1/2, thethreshold level is reduced into 1/2. Therefore, the detection of thewhite noise is not influenced by the temperature of the solid stateimage pickup device or by the operating state of the AGC circuit. In astate in which the gain of the AGC circuit rises, the object is in anenough dark state. Therefore, a specific high luminance signal of onepixel can be judged as a white spot noise.

Thus, according to the present invention, detection of white spot noisedue to defective pixels of a solid state image pickup device andcorrection based on such detection can be performed at a high precisionby the video camera itself.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more apparent from the following detaileddescription, when taken in conjunction with the accompanying drawings,in which:

FIG. 1 is a block diagram showing a construction of a main section of avideo camera according to the first embodiment of the present invention;

FIG. 2 is a flowchart showing flows of a white spot noise detectingprocess and a white spot noise correcting process according to the firstembodiment of the invention;

FIG. 3 is an explanatory diagram showing an arrangement of color filtersof a solid state image pickup device;

FIG. 4 is an explanatory diagram showing an example of a dark currentoutput of the solid state image pickup device;

FIG. 5 is a block diagram of a circuit for detecting positioninformation of pixels at which a signal is read out from the solid stateimage pickup device in the first embodiment of the invention;

FIG. 6 is an explanatory diagram showing an arrangement of color filtersof the solid state image pickup device and the signal reading-outoperation;

FIG. 7 is a block diagram of a circuit to perform a signal replacementfor a white spot noise correction in the first embodiment of theinvention;

FIGS. 8A to 8D are timing charts of the circuit of FIG. 7;

FIG. 9 is an explanatory diagram of an arrangement of color filters of asolid state image pickup device and the signal reading-out operation;

FIG. 10 is a block diagram of another circuit to perform a signalreplacement for correction of a white spot noise in the first embodimentof the invention;

FIGS. 11A to 11E are timing charts of the circuit of FIG. 10;

FIG. 12 is a flowchart showing a flow of a white spot noise detectingprocess according to the second embodiment of the invention;

FIG. 13 is a flowchart showing a flow of a white spot noise correctingprocess according to the second embodiment of the invention;

FIG. 14 is a block diagram showing a construction of a main section of avideo camera according to the third embodiment of the invention;

FIG. 15 is a flowchart showing a flow of a white spot noise detectingprocess according to the third embodiment of the invention; and

FIG. 16 is a flowchart showing flows of a white spot noise detectingprocess and a white spot noise judging process according to the thirdembodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described hereinbelowwith reference to the drawings.

FIG. 1 is a block diagram showing a construction of a video cameraaccording to the first embodiment of the invention. The video cameracomprises: a lens 101; an iris 102; a sync signal generating circuit103; a solid state image pickup device 104; an automatic gain controlcircuit (AGC circuit) 105; an analog/digital converting circuit (A/Dconverter) 106; a white spot noise correction circuit 107; a signalprocessing circuit 108; a digital/analog converting circuit (D/Aconverter) 109; and a memory 110. The light which enters from the lens 1is converted into the electric signal by the solid state image pickupdevice 104. When the brightness of an object lies within a range wherethe AGC process is necessary, namely, when the luminance signal leveldoesn't reach a predetermined value in spite of the fact that the iris102 is in a full-open state, the AGC circuit 105 amplifies the signal inaccordance with the brightness of the object. The A/D converter 106subsequently converts the amplified signal into a digital signalencompassing every pixel.

When a signal amount is less than a threshold level, the white spotcorrection circuit 107 regards that the signal is normal, so that theinput digital signal is outputted as it is. When the signal amount isequal to or larger than the threshold level, the white spot noisecorrection circuit 107 executes a predetermined correcting process. Thesignal processing circuit 108 processes the digital signal in conformitywith the standards of a video signal about the color separation, whitebalance, γ correction, and the like. The D/A converter 109 converts theinput digital signal into the analog signal and generates a luminancesignal Y and a chroma signal C.

A detecting operation of a white spot noise and a correcting operationbased on the white spot noise detection in the white spot noisecorrection circuit 107 will now be described with reference to aflowchart of FIG. 2 and FIGS. 3 to 11. In the embodiment, the white spotnoise is detected for a period of time until a picture image isdisplayed after the turn-on of a power source.

As shown in FIG. 2, the white spot noise correction circuit 107continuously allows the iris 102 to be closed after the turn-on of thepower source (step 201), thereby preventing that a photosignal entersthe solid state image pickup device 104 and also a gain of the AGCcircuit 105 is raised to make it easy to detect the white spot noise(202). In the embodiment, since the white spot noise is detected by thedigital signal, in order to also reduce a quantization error inassociation with the digitization, it is necessary to perform theamplifying process by the analog signal system before the A/D conversionis executed. It is also possible to prepare a gain setting mode which isused only for detection of the white spot noise and to set so that again in the gain setting mode only for use in the white spot noisedetection exceeds a gain variable width (i.e., an object imaging gainrange) of the ordinary operation.

In the above state (iris closing state and high gain state), the signalfrom each pixel of the solid state image pickup device 104 is read outsynchronously with a pulse which is generated from the sync signalgenerating circuit 103. FIG. 3 shows an example of an arrangement ofcolor filters of the solid state image pickup device 104. The colorfilters are constructed by filters of four colors of A, B, C, and D.Chrominance signals according to the color filters are respectively readout synchronously with horizontal and vertical driving pulses which aregenerated from the sync signal generating circuit 103. Since the iris102 is closed, however, the output from the solid state image pickupdevice 104 is constructed by only the fore-going dark current. FIG. 4shows an example of such a dark current. Although there is not so largevariation in the dark current amount of each normal pixel, the darkcurrent of a very large level such as A₁₃ is derived from the defectivepixel. Such a state is referred to as a white spot noise. The white spotnoise correction circuit 107 executes a comparison on the basis of acertain threshold level (203). The position information on the pixelwhich produces the signal of a level higher than the threshold level isstored into the memory 110 as white spot noise pixel positioninformation (204).

As for the position information, for example, such a position can beknown by counting the horizonal and vertical driving pulses. FIG. 5 is ablock diagram of a circuit to detect the position information. Thehorizonal position information is obtained by counting the horizonal (H)driving pulses by a counter 501 and by storing the count value of thecounter at a time point when the pixel is judged as a white spot noisepixel into the memory 110. The vertical position information is obtainedby counting the vertical (V) driving pulses by a counter 502 and bystoring the count value at a time point when the pixel is judged as awhite spot noise pixel into the memory 110 in a manner similar to thecase of the horizontal position information. Each of the counters 501and 502 is reset every period. That is, the counter 501 is reset by an Hreset pulse which is a pulse of the horizontal driving period. Thecounter 502 is reset by a V reset pulse which is a pulse of the verticaldriving period.

Since the video signal has been interlace scanned, it is necessary todiscriminate the presence or absence of a white spot noise from theinformation of two fields for the purpose of accuracy. In theembodiment, therefore, the presence or absence of a white spot noise ischecked as mentioned above. It is also possible to check the data of afew fields and to detect a white spot noise from the average value. Itis also possible to construct in a manner such that before checking thesignal level of every pixel, the signals of all pixels of one horizontalline are added and a signal amount is compared every horizontal line,thereby specifying the line at which a white spot noise exists, andafter that, a white spot noise is checked every one pixel with respectto such a defective line.

By the above operations, the storing process for storing the positioninformation of all pixels in which white spot noises occur into thememory 110 is finished, so that the processing routine exits from awhite spot noise pixel detecting loop (205). After that, the white spotnoise correction circuit 107 changes the gain of the AGC circuit 105 toan ordinary gain (206). Further, an image display mode is set (207),thereby executing an ordinary image displaying process. Namely, the gaincontrols of the iris 102 and AGC circuit 105 are normally executed and,while performing a proper automatic exposure, the signal is read outfrom the solid state image pickup device 104 synchronously with thepulses which are generated from the sync signal generating circuit 103.The position information of the pixels which is being read out issequentially continuously checked (208). When the position coincideswith the position of the white spot noise pixel stored in the memory110, the signal is corrected (209). The corrected signal is processed(210).

A method of correcting the signal will now be described hereinbelow withreference to FIGS. 6 to 8.

FIG. 6 shows a part of the color filters of the solid state image pickupdevice 104 shown in FIG. 3 as mentioned above. The signals aresequentially read out in accordance with the order from the left edge.It is now assumed that a defective pixel occurs in the pixel of thecolor filter A₁₂ and its position information has been stored in thememory 110. In the embodiment, a correcting method of replacing thesignal of A₁₂ by the signal of B₁₁ is used as an example of a correctingmethod of the signal.

FIG. 7 is a block diagram showing a circuit for such a signalreplacement. Such a circuit comprises a switch 701 and a D flip-flop(D·F/F) 702. The signal which is handled by the white spot noisecorrection circuit 107 is a digital signal and the signal of each pixelwhich is derived from the solid state image pickup device 104 is alsoprocessed by a plurality of bits. The white spot noise correctioncircuit 107 is provided for one of a plurality of bits.

FIGS. 8A to 8D are timing charts of the circuit block of FIG. 7. TheD·F/F 702 performs a delay operation by a clock CK1 (FIG. 8A) of thesame speed as the timing to read out the signal from the solid stateimage pickup device 104. When the clock input is stopped, the D·F/F 702holds the output data in accordance with its characteristics. Therefore,by turning off the switch 701 by a control pulse (FIG. 8B), the clockCK1 is not supplied to the D·F/F 702 and the output data can be replacedwith the data of the previous pixel. That is, by setting the controlpulse to the low level in accordance with the position informationstored in the memory 110, the data on A₁₂ having a white spot noise canbe replaced by B₁₁. It will be obviously understood that when the clockCK1 is at the high level, the data is not replaced.

In the circuit of FIG. 7, the defective pixel is merely replaced by theinformation on the previous pixel. However, the defective pixel can bealso replaced by the signal of the same color filter. A signalcorrecting method for this purpose will now be described hereinbelowwith reference to FIGS. 9 to 11.

FIG. 9 shows a part of the color filters of the foregoing solid stateimage pickup device 104 shown in FIG. 3 in a manner similar to FIG. 6.The signals are sequentially read out in accordance with the order fromthe left edge. It is also assumed here that defective pixel also occursin the pixel of the color filter A₁₂ and its position information hasbeen stored in the memory 110.

FIG. 10 is a block diagram showing another circuit for signalreplacement. The circuit comprises: D flip-flops (D·F/F) 1001 to 1004each for delaying the input data by the clock CK1; a change-over switch1005; an adding circuit 1006; and a dividing circuit 1007 for reducing adata value into 1/2. According to the circuit, as a signal correctingmethod, when a defective pixel occurs in the pixel of the color filterA₁₂, the information of A₁₂ is replaced by the average value of thesignals of A₁₁ and A₁₃.

FIGS. 11A to 11E show timing charts of the signals in FIG. 10. Sinceeach of the D·F/F 1001 to 1004 delays the data synchronously with theclock CK1 (FIG. 11A), a timing of the input data (FIG. 11C) of the D·F/F1001 and a timing of the output data (FIG. 11D) of the D·F/F 1004 are asshown in FIG. 11. In the circuit of FIG. 10, the change-over switch 1005is switched to the dividing circuit 1007 side for a period of timeduring which the control pulse (FIG. 11B) is set to the high level onthe basis of the white spot noise information in the memory 110. Aninput of the D·F/F 1003 is connected to an output of the dividingcircuit 1007. Thus, the signal of A₁₂ is replaced with the average valueof A₁₁ and A₁₃. Since the circuit corrects the white spot noise by thesignal of the same color filter, the generation of a false color issuppressed.

According to the first embodiment as described above, a white spot noiseis detected in a state in which the iris 102 is closed and the darkcurrent as an output of the solid state image pickup device 104 issufficiently amplified by the AGC circuit 105. Thus, the detection of awhite spot noise and the correction based on it can be accuratelyexecuted by the video camera itself.

The second embodiment will now be described with reference to flowchartsof FIGS. 12 and 13. In the ordinary video camera, it is common sense inthe power off state that the iris is closed so that the solid stateimage pickup device is not burnt by the light from the lens. In theordinary video camera, therefore, the system including the iris is setinto a predetermined state at the time of power-off and, after that, thepower source is turned off. According to the second embodiment,therefore, a white spot noise is detected for a period of time duringwhich the power source of the circuit is finally turned off after theiris was closed.

FIG. 12 is a flowchart of the white spot noise correction circuit 107for detection of a white spot noise. When the operation to turn off thepower switch is detected (1201), the white spot noise correction circuit107 allows the iris 102 to be closed (1202) and increases the gain ofthe AGC circuit (1203). The white spot noise correction circuit 107subsequently executes processes for detecting and storing the positioninformation of all pixels having white spot noises of the solid stateimage pickup device 104 in steps 1204 to 1206 in a manner similar tosteps 203 to 205 in FIG. 2 mentioned above. After that, the white spotnoise correction circuit 107 returns the gain of the AGC circuit 105 tothe normal mode (1207). The power source is turned off after that(1208).

FIG. 13 is a flowchart for white spot noise correction. Descriptions ofprocessing steps 1301 to 1304 of the flow are omitted because thoseprocesses are similar to those in steps 207 to 210 in FIG. 2 mentionedabove.

An object of the second embodiment is also to accurately detect a whitespot noise by closing the iris and increasing the gain of the AGCcircuit in a manner similar to the first embodiment. According to thesecond embodiment, when the power source is turned on, the positioninformation on the white spot noise has already been stored in thememory and the correction of the white spot noise is executed on thebasis of the position information stored. Therefore, a time which isrequired until a picture image is actually displayed after the turn-onof the power source can be reduced from that in the first embodiment.According to the second embodiment, since a white spot noise is detectedin a state in which each section of the video camera is sufficientlywarmed and the circuit system and the like are stabilized, a detectionprecision of a white spot noise is further raised. In the secondembodiment, the memory 110 to store the white spot noise positioninformation needs to be backed up by a sub-battery or the like differentfrom a main power source battery even when the main power source is shutoff. In both of the first and second embodiments, the contents in thememory 110 are reset before the white spot noise is detected.

The third embodiment will now be described with reference to FIGS. 14and 15. In the third embodiment, a white spot noise is detected in astate in which the iris is completely opened and the gain of the circuitsystem is raised. The third embodiment intends to detect and correct awhite spot noise even in a state in which an object is actually beingphotographed. Although the third embodiment can be solely constructed,it is desirable to combine it with the first or second embodiment.

FIG. 14 shows a block diagram of a main section of the video cameraaccording to the second embodiment. The video camera comprises: a lens1401; an iris 1402; a sync signal generating circuit 1403; a solid stateimage pickup device 1404; an AGC circuit 1405; an A/D converting circuit1406; a white spot noise correction circuit 1407; a signal processingcircuit 1408; a D/A converting circuit 1409; a memory 1410; and atemperature detecting circuit 1411. A description of a series of signalprocesses of the sync signal generating circuit 1403, solid state imagepickup device 1404, AGC circuit 1405, A/D converter 1406, signalprocessing circuit 1408, D/A converter 1409, and memory 1410 is omittedbecause it is similar to that of the video camera shown in FIG. 1.

FIG. 15 shows an operation flow of the white spot noise correctioncircuit 1407. First, the white spot noise correction circuit 1407 checksthe white spot noise position information which has already been writtenin the memory 1410 (1501). When there is white spot noise positioninformation, the white spot noise is corrected on the basis of theposition information (1502). After that, the white spot noise correctioncircuit 1407 obtains the AGC gain data from the AGC circuit 1405 (1503)and further obtains the data of a temperature of the solid state imagepickup device 1404 or its peripheral temperature from the temperaturedetecting circuit 1411 (1504). A threshold level of the white spot noiseis calculated (1505). The threshold level is calculated by arithmeticoperations such that when the gain of the AGC circuit is doubled, thethreshold level is also doubled, and when the gain of the AGC circuit isreduced into 1/2, the threshold level is also decreased into 1/2, and onthe other hand, when the temperature is raised by 10° C., the thresholdlevel is doubled and, when the temperature decreases by 10° C., thethreshold level is reduced into 1/2. The white spot noise correctioncircuit 1407 checks the white spot noise pixel by using the calculatedthreshold level (1506). The position information on the pixel which wasdetermined to be a pixel having a white spot noise is newly written intothe memory 1410 (1507). A sudden large signal of only one pixel isjudged as a white spot noise and the detected white spot noise iscorrected within the next frame. The processing orders of the white spotnoise detecting process and correcting process can be also reversed.

A problem which occurs when the white spot noise is corrected in theordinary photographing state relates to at which accuracy the white spotnoise signal is discriminated. That is, it is important to correctlydetermine whether the large signal obtained is caused by the photosignalwhich enters the solid state image pickup device 1404 or by the whitespot noise. As mentioned above, by allowing the threshold level to beadapted to the temperature of the solid state image pickup device 1404or to the operating state of the AGC circuit and by regarding the suddenlarge signal of only one pixel as a white spot noise, an enough effectcan be obtained. However, by adding a process to again discriminatewhether the pixel which was judged as a white spot noise continues for apredetermined time or the signal is a large signal which can be alsoregarded as a white spot noise even after the elapse of thepredetermined time, the detection precision of the white spot noise canbe further improved.

FIG. 16 shows a processing flow for executing the checking operations aplurality of times. In a manner similar to the flow of FIG. 15, thewhite spot noise correction circuit 1407 checks the gain and temperature(1601), calculates the threshold level (1602), and detects the whitespot noise pixel (1603). Further, in the case where the white spot noisepixel is detected, the white spot noise correction circuit 1407 recordsthe white spot noise and the number N of detection times into the memory1410 with respect to each pixel (1604). When the number of detectiontimes of the white spot noise reaches a predetermined number of times N₀or more with regard to the same pixel, namely, when N>N₀ (1605), thecorrection is executed for the first time (1606). According to the flow,since the correction is executed when the number of detection times ofthe white spot noise reaches the predetermined plural number N₀ or more,the detection precision of the white spot noise is further improved. Therecorded number N of detection times is reset when the power source isturned on.

Although the present invention has been described above with respect tothe preferred embodiments, many various modifications are possiblewithin the scope of the claims of the invention without departing fromthe spirit and idea of the present invention. It will be also obviouslyunderstood that the invention can be embodied by combining the aboveembodiments.

What is claimed is:
 1. A video camera comprising:a lens system forforming an image from an incident light; a solid state image pickupdevice for converting the image of an object formed by said lens systeminto an electric signal corresponding to a plurality of pixels; a lightshielding means for shielding the incident light to said solid stateimage pickup device; a detecting means for comparing an output signal ofeach pixel of the solid state image pickup device and a predeterminedlevel, thereby detecting defective pixels of the solid state imagepickup device; a means for controlling said light shielding means so asto shield the incident light to said solid state image pickup devicewhen said detecting means detects defective pixels; an automatic gaincontrol circuit amplifying an output of said solid state image pickupdevice with an object imaging gain within an object imaging gain rangefor keeping a brightness of the image constant during times when theimage of said object is formed, and with a defective pixel detectinggain during times when said detecting means detects said defectivepixels, wherein said defective pixel detecting gain has a gain levelwhich is higher than a highest gain level of said object imaging gainrange; a means for raising a gain of said automatic gain control circuitto said defective pixel detecting gain during times when said detectingmeans detects said defective pixels; a memory for storing positioninformation on said defective pixels detected by said detecting means;and a replacing means for replacing a signal of a defective pixel ofsaid defective pixels, which is specified by said position informationin said memory by a signal formed based on a signal of a peripheralpixel of said defective pixel, wherein said detecting means detects saiddefective pixels in a state in which the incident light is shielded bysaid light shielding means.
 2. A video camera according to claim 1,wherein the signal formed based on the signal of the peripheral pixel ofsaid defective pixel is a signal of a pixel adjacent to said defectivepixel.
 3. A video camera according to claim 1, wherein the peripheralpixel of said defective pixel is a pixel existing at a nearest positionfrom among pixels having color filters of a same color as that of acolor filter of said defective pixel.
 4. A video camera according toclaim 1, wherein the detection of said defective pixels by saiddetecting means and the light shielding of the incident light by saidlight shielding means are automatically executed after a power source isturned on.
 5. A video camera according to claim 1, wherein the detectionof said defective pixels by said detecting means and the light shieldingof the incident light by said light shielding means are automaticallyexecuted when an operation to shut off a power source is performed.
 6. Amethod of correcting a defect of a signal which is output for aplurality of pixels from a solid state image pickup device, comprisingthe steps of:shielding an incident light to said solid state imagepickup device by a light shielding means; using an automatic gaincontrol circuit to amplify an output of said solid state image pickupdevice with a an object imaging gain within an object imaging gain rangefor keeping a brightness of the image constant during times when theimage of said object is formed, and with a defective pixel detectinggain during times when defective pixels are detected, wherein saiddefective pixel detecting gain has a gain level which is higher than ahighest gain level of said object imaging gain range; detecting saiddefective pixels of the solid state image pickup device while saidautomatic gain control circuit amplifies said output with said defectivepixel detecting gain by comparing an output signal of each pixel of saidsolid state image pickup device and a predetermined level; storingposition information on said defective pixels detected by said detectingstep; opening said light shielding means; and replacing a signal of thedefective pixel which is specified by said position information storedby a signal formed based on a signal of a peripheral pixel of saiddefective pixel.
 7. A method according to claim 6, wherein the signalformed based on the signal of the peripheral pixel of said defectivepixel is a signal of a pixel adjacent to said defective pixel.
 8. Amethod according to claim 6, wherein the peripheral pixel of saiddefective pixel is a pixel existing at a nearest position from amongpixels having color filters of a same color as that of a color filter ofsaid defective pixel.
 9. A method according to claim 6, wherein thelight shielding of said incident light is automatically executed after apower source is turned on.
 10. A method according to claim 6, whereinthe light shielding of said incident light is automatically executedwhen an operation to shut off a power source is performed, and theopening of said light shielding means is automatically executed afterthe power source is turned on.
 11. A video camera according to claim 6,wherein the detection of said defective pixels by said detecting stepand the light shielding of the incident light by said light shieldingmeans are automatically executed when an operation to shut off a powersource is performed.
 12. A method of correcting a defect of a signalwhich is output for a plurality of pixels from a solid state imagepickup device, comprising the steps of:multiplying a predeterminedreference value by a coefficient corresponding to a value of a gain ofan automatic gain control circuit for amplifying an output of said solidstate image pickup device so as to keep a brightness of an imageconstant to obtain a reference level; detecting defective pixels of thesolid state image pickup device by comparing an output signal of eachpixel of the solid state image pickup device which was amplified by saidautomatic gain control circuit and said reference level; storingposition information for ones of said defective pixels which, for apredetermined number of occurrences, satisfy a criterion that an outputsignal of a pixel corresponding to a defective pixel is greater thansaid reference level and output signal levels of pixels located beforeand after a defective pixel are not greater than said reference level;and replacing the signal of the defective pixel which is specified bythe position information stored by a signal formed based on a signal ofa peripheral pixel of said defective pixel.
 13. A method according toclaim 11, wherein when the gain of said automatic gain control circuitis doubled, said reference level is substantially doubled and, when thegain of the automatic gain control circuit is reduced into 1/2, saidreference level is decreased into substantially 1/2.
 14. A methodaccording to claim 11, wherein the signal formed based on the signal ofthe peripheral pixel of said defective pixel is a signal of the pixeladjacent to said defective pixel.
 15. A method according to claim 12,wherein the peripheral pixel of said defective pixel is a pixel existingat a nearest position from among pixels having color filters of a samecolor as that of a color filter of said defective pixel.